27.25 inch wheel to 700c wheel

[big Pete]

Hi all,
I want to put new wheels on my bike. But the standard it uses is 27.25
inch. How simple is it to put on 700c wheels. I did the math and 700c
is about 27.55 inches. But when I put in an extra 700c wheel I had, the
brake pads would not reach the rim (half the pad was on the rim the
other half was on the tire). The bike I am working on is a Peugeot
Supper Sport from early 80's. I have two questions:

1) Why did the pads not reach? I know I can get long reach brakes to
solve the problem but I still think they should of reached the rim.

2) Are my assumptions good? I am assuming 700c means that the wheel
diameter is 700mm or 70cm.

Thank you very much

Pete

--
big Pete

[carl...@comcast.net]

Dear Pete,

Regrettably, you have been misled by a wicked conspiracy that Sheldon
Brown has exposed in detail:

http://www.sheldonbrown.com/tire-sizing.html

Briefly, that 700c means the nominal tire size, not the rim.

The rim is 622mm.

Cheers,

Carl Fogel

[Rick]

Carl, in his inimitable style, has given you a hint and a pointer to a
page by Sheldon. But the quick and easy answer is:

27" wheel has a rim with a 630mm BSD
700c wheel has a rim with a 622mm BSD

i.e., 700c rim is 8mm less in diameter than a 27" wheel, so you brakes
pads
would need to move down towards the hub by 4mm (1/2 of 8mm). If your
pads
cannot move down that far then you would need brakes with a longer
reach
to make the conversion. Sounds like you are out of luck unless you
want to replace the brake calipers.

- rick

[Art Harris]

big Pete wrote:

> But when I put in an extra 700c wheel I had, the
> brake pads would not reach the rim (half the pad was on the rim the
> other half was on the tire).

I assume you tried loosening the brake pads and moving them lower in
the caliper slot? If so, it sounds like you need longer reach brakes.
Actually, your bike probably has what were called "standard reach"
brakes but which are referred to as "long reach" today.

A drop bolt is another possibility.

http://www.sheldonbrown.com/home-drop.html

Art Harris

[Ernie Willson]

Sometimes you can adjust (read bend) the brake arm to make up this
difference (not recommended). Alternately you can buy a special bolt
that will drop the caliper the required 4mm.

HTH,
EJ in NJ

[Art Harris]

Also, read about brake reach and how to measure it at:

http://www.sheldonbrown.com/gloss_ra-e.html#reach

Art Harris

[data...@yahoo.com]

buy a new round rat tail file
shud be enough room or metal to use the old centerpulls with 700c rims
tho it may not appear thus when eyeballing the proposed setup

an aluminum plate is needed to lower newer and desirable sidepulls

[A Muzi]

They are _nominal_ dimensions-- like dress sizes.

27" systems are 630mm, 70C systems are 622mm, which is about 6mm radius.

Peugeot Supper Sport? Part of the "three squares" series???
--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

[ron]

700c is supposedly 4mm less in radius (though I think the actual
difference may be a bit more than that). Other options:

1. Stick with 27" - it is still possible to get/build decent 27" wheels
and there are still some OK 27" tires made (Conti Ultragatorskins
aren't bad).

2. Scrounge for some longer reach old school brake calipers that will
reach 700c rims from your frame. Brake calipers are not all the same, by
any means.

3. Replace the fork with a 700c unit (meaning you can run a standard,
modern dual pivot front brake) and go fixed gear so you don't need a rear
brake at all. The shorter fork will slightly change the front end
geometry, but not necessarily for the worse. Forks can be pretty cheap.
You can go to a carbon fork and threadless headset at the same time (if
you don't care too much about a pure retro look), which will give you a
lot more choice of stems (and in my experience the threadless setup tends
to be a lot stiffer and trouble free than most threaded assemblies). You
would need a fork, stem, headset and brake to go this route, so it would
add up.

4. Make a drop bolt assembly. I made one once (for the rear brake) from
a short piece of 3/4" square-section steel tubing, and some canibalized
brake hardware. Worked great. Front brake drop bolt would have more
stress though, and be more critical (I would be leery of using a drop bolt
on a front brake).

[Qui si parla Campagnolo]

big Pete wrote:
> Hi all,
> I want to put new wheels on my bike. But the standard it uses is 27.25
> inch. How simple is it to put on 700c wheels. I did the math and 700c
> is about 27.55 inches. But when I put in an extra 700c wheel I had, the
> brake pads would not reach the rim (half the pad was on the rim the
> other half was on the tire). The bike I am working on is a Peugeot
> Supper Sport from early 80's. I have two questions:
>
> 1) Why did the pads not reach? I know I can get long reach brakes to
> solve the problem but I still think they should of reached the rim.

27 inch is larger than 700c...Like you said get lomg reach brakes and
bob's yer uncle.